One of the most common issues causing connectivity problems with GRID Test Drive is port and protocol blocking at your firewall. Please use Telnet or a similar tool to confirm port access.
The ports you’ll need opened are:
47991, 47995, 47996, 47998, 47999, 48000, 35043, 42231, 443 and 5001
These ports need to be enabled for both UDP and TCP traffic.